"PCMCIA" stands for the Personal Computer Memory Card International Association. PCMCIA cards, element 1 in FIGS. 1, 2, 3, and 4, are the "credit card" peripherals used as memory cards, including DRAM, SRAM, ROM, and PROM cards, modem-fax cards, mini-hard drive cards, terminal emulator cards, and the like. They are built to a PCMCIA standard. The PCMCIA standard sets the electrical, mechanical, and interface requirements for PCMCIA cards.
The small size of PCMCIA cards is intended to meet the form factor demands of portable computers. These small cards are approximately the size of a plastic credit card (54.0 mm by 85.6 mm) but several times thicker (Type I PCMCIA cards are 3.3 mm thick, Type II PCMCIA cards are 5 mm thick). It should be noted that, as used herein, Type I and Type II refer to the PCMCIA form and fit type standards, and not to the method of surface mount device attachment. PCMCIA cards are described in, for example, R. C. Alford, "Under The Hood: The PCMCIA Redefines Portability", Byte Magazine, December 1992, pp. 237-242; by Ken Ueltzen "Pushing The Packaging Envelope", Circuit Assembly, March 1992, pp. 32-35, and Richard Nass, "IC-Card Spec Adapts I/O To Memory Card Slot," Electronic Design, Jan. 22, 1992, pp. 45-57.
A PCMCIA card is shown in FIG. 1, a partial cutaway view of a PCMCIA card, with the top cover removed, is shown in FIG. 2, a cutaway side elevation of a PCMCIA card is shown in FIG. 3, and an exploded view of a PCMCIA card is shown in FIG. 4. The perspective views of a PCMCIA card show the top cover on 11 and off, and the 68 contact interface connector 21. FIG. 2 shows a PCMCIA card opened up without a top cover, to show the IC chips., and FIG. 3 shows a side elevation in cutaway with the PCMCIA's interface 21, the cover-frame assembly 31, an optional insulator sheet 41, and a printed circuit board 23 populated with IC chips 25 on both sides. The card 1 has a top cover 11, a frame 31, a printed circuit board 23, and a bottom cover 15.
To be noted is that the contacts 21 (standard PCMCIA) are at one end of the PCMCIA card 1 and the printed circuit card 23. According to the now current PCMCIA Standard 2, this is a 68 contact strip, with a width of 2 inches. The card 1 itself is 3.3 millimeters thick from top cover 11 to bottom cover 15, with the top cover 11 and bottom cover 15 having a total combined thickness of just 0.4 millimeters. This allows 2.9 millimeters of thickness for a populated, double sided, printed circuit card 23.
The height limitations of Type I cards, 3.3 mm, requires the use of low profile technologies, for example, either tape automated bonding (TAB) or card-on-board (COB) packaging technologies, both with specially designed low height IC chips 25, as TSOP IC chips 25. The thin, small outline package (TSOP) IC chip 25, with a height of 1.2 mm (0.047 inch), is particularly desirable for double sided Type I PCMCIA cards 1. Its low profile allows population of both sides of the PCMCIA printed circuit card 23 as shown in FIG. 3.
In an alternative IC chip technology a paper thin small outline package (PTSOP) having a height of just 0.5 mm (0.020 inch) is utilized, allowing two printed circuit cards 23 to be carried in a single PCMCIA card package 1. The lead pitch for TSOP IC chips is 0.5 mm (0.019 inch). Memory printed circuit cards are populated with 0.019 inch to 0.025 inch lead pitch IC chips, with approximately 1000 solder joints per printed circuit card 23. The surface mount technology required for the printed circuit boards 23 in Type I PCMCIA cards 1 comprises the steps of screen or stencil printing the solder paste onto the raw printed circuit card 23, chip 25 placement, and reflow.
The standard process flow is shown in FIG. 5.
The fine pitch requirements noted above, combined with fast cycle times, mandate automated cleaning of the solder paste stencil or screen, as well as solder paste deposition forms and patterns for proper solder joint formation. The fine pitch also requires that solder paste dispensing must be precisely controlled to avoid both solder bridging and solder gaps. The fine pitch further requires special handling of the in-process printed circuit boards in the critical interval between IC chip placement and solder reflow to avoid movement, misalignment, and misregistration of the SMT IC chips, which are held in place solely by the tackiness of the solder paste carrier.
The placement equipment required for placing TSOP IC chips 25 onto a high circuit density printed circuit card 23 requires high accuracy. In populating PCMCIA cards tape and reel is a preferred method used to supply properly aligned chips and devices, although pick and place tooling is also used for placement, as are machine vision robotic tools.
Reflow is carried out in a conveyorized system to avoid contamination or movement of devices.
Testing of populated cards 23 is driven by the number of leads, the pitch, and the interconnect density. Typically testing is performed through the edge connectors, e.g., the 68 contact PCMCIA standard interface 21, by boundary testing devices, although "bed of nails" testers can be utilized.
While the general process flow of the prior art used for PCMCIA fabrication is shown in FIG. 5 for a chip directly attached to a circuitized board, it is to be noted that Tape Automated Bonding (TAB) and Chip-On-Board (COB) joining may also be used in PCMCIA cards. In COB joining aluminum wire bonding is used. This avoids the high temperatures associated with gold wire bonding. After wire bonding a thermally curable epoxy glob top is placed atop the chip.
The PCMCIA standard specifies standards for the card controller and the card device driver. The PCMCIA card controller standard, without pin numbers, is shown in FIG. 6. This shows the contact names and functions of the host interface, the contact names and functions of the PCMCIA card interface, and the components, names, and functions of the PCMCIA card controller.
The PCMCIA standard further specifies aspects of the operating system, BIOS, and device driver interfaces. These are shown in FIG. 7.
The high functionality per unit area results in a high circuit density and a very high wiring density, demanding precise alignment and registration maintenance throughout the manufacturing process. Maintenance of alignment and registration, combined with one or two solder reflow thermal processing steps requires special package designs, fabrication equipment, and fabrication processes.
Thus a need exists for efficient manufacturing apparatus and processes that avoid thermally induced damage to in-process cards and boards.